The lubes unit extracts high-viscosity heavy material from VGO and vac resid to produce base oils. Base oils are the blend stocks for producing finished lubricating oils such as motor oil.

Base oils are a specialty product of very high value. So even thought the volumes of base oil produced in a plant may be very small, it can contribute significantly to overall refinery profitability. However, the capital cost per barrel of lubes plants is relatively high so only a subset of refineries have installed them.

The lubes or base oil plant typically consists of several different steps of processing, though not all plants will have all of the steps. These include:

Propane deasphalting - a solvent extraction process that uses propane to separate asphaltenes and other undesirable material from vacuum resid to yield base oil.

Lubes aromatics extraction - a solvent extraction process that uses furfural, phenol or NMP to extract aromatics from VGO or deasphalted vac resid.

Dewaxing - a solvent extraction process that uses ketone (or sometimes propane) to remove wax from base oil.

Lubes hydrocracking - selective hydrocracking of aromatics-extracted base oil to reduce pour point and to crack waxy molecules.

Lubes hydrotreating - mild hydrotreating of base oil to improve color and stability by removing chemically active compounds